An exhaust gas sensor may be positioned in an exhaust system of a vehicle for detecting an air-fuel ratio of the gas exhausted from an internal combustion engine. For example, the exhaust gas sensor readings may feedback to a controller for adjusting the air-fuel ratio of the engine by modifying the amount of fuel injector from a fuel injector of the engine.
Degradation of the exhaust gas sensor may cause engine control degradation resulting in increased emissions and/or reduced vehicle drivability. In particular, an exhaust gas sensor may exhibit numerous discrete types of degradation. The sensor degradation types may be grouped into filter type degradation and delay type degradation. Further, the sensor degradation types may either be symmetric or asymmetric. For example, a sensor with asymmetric type sensor degradation may have different response dynamics (such as response time or response rate) when the sensor response increases versus when the sensor output decreases.
Previous approaches for addressing the sensor degradation includes equipping the exhaust gas sensor with an anticipatory controller for correcting or compensating for the degradation. For example, parameters of the anticipatory controller may be adjusted based on the type of sensor degradation. Further, to maintain stability of the anticipatory controller system, gains of the feedback control routine of the controller, such as a proportional/integral control routine, may be reduced aggressively to reduce system instability.
However, the inventors herein have recognized potential issues with such systems. For example, adjusting parameters of the anticipatory controller may not address the asymmetric dynamics of the sensor response during rich-to-lean and lean-to-rich transitions. This may result in asymmetric engine operation when a commanded air-fuel ratio transitions in different directions (e.g. the rich-to-lean direction and the lean-to-rich direction). As a result, more or less fuel may be delivered in the direction of the degradation, and CO or NOx emission may be increased.
In one example, the issues described above may be addressed by a method comprising sensing an air-fuel ratio via an exhaust gas sensor; responsive to an asymmetric sensor response, generating a modified air-fuel ratio with a symmetric response based on the sensed air-fuel ratio; and adjusting fuel injection based on the modified air-fuel ratio. In this way, the anticipatory controller may compensate the sensor degradation similarly when the commanded air-fuel ratio transits in both the rich-to-lean and lean-to-rich directions, and the asymmetric engine operation may be reduced.
As one example, a method may comprise operating an engine with a commanded air-fuel ratio, and determining the type and magnitude of sensor degradation by comparing the sensed air-fuel ratio with a commanded air-fuel ratio. The exhaust gas sensor may be determined to have asymmetric type sensor degradation when a response rate and/or a response time of the sensor response is different responsive to the commanded air-fuel ratio transitioning in different directions (e.g., rich-to-lean direction or lean-to-rich direction). The exhaust gas sensor may exhibit symmetric type sensor degradation if the response rate and response time are the same responsive to the commanded air-fuel ratio transitioning in different directions, while the response rate or the response time is different from an expected value. Responsive to the asymmetric type sensor degradation, a modified sensor response may be generated by introducing a lower response rate and increased response time (e.g., modifying the sensor reading to be symmetric) as compared to the un-faulted portion of the sensed air-fuel ratio. As such, the modified sensor response may have the same response rate and/or the response time when the commanded air-fuel ratio transitions in each of the increasing and decreasing directions. As such, the modified sensor response is more symmetric comparing to the sensed air-fuel ratio. The modified sensor response may then be fed to an anticipatory controller with parameters adapted based on the sensor degradation. In this way, the anticipatory controller may operate more symmetrically and effectively to address sensor degradation during both rich-to-lean and lean-to-rich transitions. Further, calibration work of the controller may be reduced, and NOx and CO emissions of the engine may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.